Activation of microvascular endothelial cells in active ulcerative colitis and detection of inducible nitric oxide synthase

Differences in the mechanism of nitric oxide production between mouse vascular endothelial cells and macrophages

The detailed mechanism of NO production in mouse vascular endothelial cells, END-D, was studied. The NO production in END-D cells was triggered by gamma interferon (IFN-γ), but not LPS. However, LPS augmented the NO production in IFN-γ-stimulated END-D cells. A high level of NO production was due to the expression of an inducible type of NO synthase (iNOS) in those cells. A significant amount of NO was detected 18 h after IFN-γ stimulation, accompanied by the delayed iNOS expression. The JAK/STAT signal pathway mediated IFN-γ-induced NO production, but did not participate in the LPS-induced augmentation. Further, no activation of nuclear factor (NF)-κB was involved in the NO production in END-D cells stimulated with either IFN-γ and/or LPS. The mechanism of NO production in END-D cells was suggested to be different from that in mouse macrophages. The differential regulation of NO production in mouse vascular endothelial cells and macrophages is discussed.

Effect of IBD sera on expression of inducible and endothelial nitric oxide synthase in human umbilical vein endothelial cells

AIM: To study the expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS) and their role in inflammatory bowel disease (IBD).

METHODS: We examined the effect of sera obtained from patients with active Crohn’s disease (CD) and ulcerative colitis (UC) on the function and viability of human umbilical vein endothelial cells (HUVEC). HUVECs were cultured for 0-48 h in the presence of a medium containing pooled serum of healthy controls, or serum from patients with active CD or UC. Expression of eNOS and iNOS was visualized by immunofluorescence, and quantified by the densitometry of Western blots. Proliferation activity was assessed by computerized image analyses of Ki-67 immunoreactive cells, and also tested in the presence of the NOS inhibitor, 10^-4 mol/L L-NAME. Apoptosis and necrosis was examined by the annexin-V-biotin method and by propidium iodide staining, respectively.

RESULTS: In HUVEC immediately after exposure to UC, serum eNOS was markedly induced, reaching a peak at 12 h. In contrast, a decrease in eNOS was observed after incubation with CD sera and the eNOS level was minimal at 20 h compared to control (18% ± 16% vs 23% ± 15% P<0.01). UC or CD serum caused a significant increase in iNOS compared to control (UC: 300% ± 21%; CD: 275% ± 27% vs 108% ± 14%, P<0.01). Apoptosis/necrosis characteristics did not differ significantly in either experiment. Increased proliferation activity was detected in the presence of CD serum or after treatment with L-NAME. Cultures showed tube-like formations after 24 h treatment with CD serum.

CONCLUSION: IBD sera evoked changes in the ratio of eNOS/iNOS, whereas did not influence the viability of HUVEC. These involved down-regulation of eNOS and up-regulation of iNOS simultaneously, leading to increased proliferation activity and possibly a reduced anti-inflammatory protection of endothelial cells.

Gestational diabetes and the adenosine/L-arginine/nitric oxide (ALANO) pathway in human umbilical vein endothelium

Altered endothelial cell function is a key factor associated with vascular disorders and is critical in the fetal growth and development. Pregnancies affected by diseases such as gestational diabetes are associated with human umbilical vein endothelial dysfunction, a finding that has been associated with a high incidence of vascular complications during the adult life. Limited information is available addressing cellular mechanisms associated with altered human umbilical vein endothelial function in gestational diabetes. One of the key signalling pathways associated with altered vascular physiology is the synthesis of the vasodilator nitric oxide (NO) from the cationic amino acid L-arginine by the endothelium (i.e. the endothelial L-arginine/NO pathway). The activity of this signalling pathway is modulated by D-glucose, adenosine, insulin, and ATP, among other molecules, and is upregulated (transcriptional, post-transcriptional and post-translational levels) in gestational diabetes. This review focuses on the cellular and molecular mechanisms involved with elevated adenosine levels in fetal umbilical vein blood and the endothelial L-arginine/NO pathway activity in gestational diabetes. We suggest that a lower capacity of adenosine transport by the fetal endothelium in gestational diabetes leads to extracellular accumulation of this nucleoside and its higher bio-availability activates endothelial P1 type purinoceptors. A functional association between A2a purinoceptor subtype signalling and the activity of the l-arginine transport mediated by human cationic amino acid transporters and endothelial NO synthase activity (i.e. 'ALANO pathway') is proposed, revealing in part the mechanisms that account for human umbilical vein endothelial cell dysfunction programmed through the development of the fetus in gestational diabetes.

Expression of nitric oxide synthase 2 and tumor necrosis factor alpha in swine naturally infected with Actinobacillus pleuropneumoniae

Nitric oxide synthase 2 (NOS2) and tumor necrosis factor alpha (TNF-alpha) were detected and localized in 15 pigs with naturally occurring pleuropneumonia by use of in situ hybridization with a nonradioactive digoxigenin-labeled cDNA probe. Two cDNA probes 491 and 219 base pairs for NOS2 and TNF-alpha, respectively, were generated by reverse transcription polymerase chain reaction. All 15 pigs infected with Actinobacillus pleuropneumoniae had distinct positive hybridization signals for NOS2 and TNF-alpha. Strong hybridization signals for both NOS2 and TNF-alpha were evident in degenerate alveolar leukocytes bordering zones of coagulative necrosis and in alveolar spaces. NOS2 nucleic acids were detected in neutrophils and macrophages. In situ hybridization of serial sections of lung tissue revealed numerous cells positive for NOS2 and TNF-alpha, suggesting that NOS2 and TNF-alpha expression may play a role in the pathophysiology of pleuropneumonia.

The sympathetic adrenomedullary system, but not the hypothalamic-pituitary-adrenal axis, participates in aorta adaptive response to stress: nitric oxide involvement

Stress induced a decrease in the reactivity of the aorta to noradrenaline (NA), as a consequence of an endothelial nitric oxide (NO) system hyperactivity. The main characteristic of the stress response is activation of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic adrenomedullary (SA) system. The participation of the HPA axis and SA system in the decreased reactivity to NA in the aorta of rats exposed to 4-h immobilization was investigated. Concentration-response relationships for NA were obtained in the aorta, with and without endothelium, isolated from normal and stressed rats, following these procedures: (1) in the absence and presence of L-NAME; (2) after adrenalectomy (ADX) or not, in the absence or presence of L-NAME; (3) ADX rats treated or not with corticosterone; (4) ADX associated with stress; and (5) treated or not with reserpine. The reactivity of aorta without endothelium was unaffected by the procedures. The reactivity of aorta with endothelium was decreased by either stress or ADX. This effect was reversed by both L-NAME and corticosterone. ADX did not potentiate the decrease in the aorta reactivity induced by stress. Reserpine did not change the reactivity of aorta with endothelium from normal rats, but prevented the decrease in reactivity induced by stress. It is concluded that the HPA axis participates in endothelium-dependent modulation of aorta reactivity in normal conditions and that the SA system participates in hyperactivity of the endothelial NO-system induced by stress, which is responsible for the decreased aorta reactivity to NA.

Immunology of inflammatory bowel disease

The immunology of inflammatory bowel disease continues to be an intense area of investigation for clues to the pathogenesis of Crohn disease and ulcerative colitis. As typical with complex diseases, inflammatory bowel disease research is continuously evolving. Without abandoning traditional areas of study, such as humoral and cellular immunity and cytokines, investigation is broadening to explore new molecules and biologic phenomena. Novel cytokines and cell adhesion molecules appear to be involved in inflammation, while the role of nitric oxide is being clarified. Leukocyte resistance to apoptosis appears to be a major contributing factor to Crohn disease. Epithelial cell-derived defensins and receptors are arising as key molecules mediating the interaction of innate and acquired mucosal immunity with the enteric flora, and explaining how the latter participates in gut inflammation. The results of these combined studies are opening novel therapeutic horizons whose implementation offers better forms of treatment.

Expression of the inducible isoform of nitric oxide synthase in pigment cell lesions of the skin

Nitric oxide (NO) is a small molecule produced during the conversion of L-arginine to L-citrulline by NO synthase (NOS). Several isoforms of NOS exist, of which the Ca2+-independent, inducible NOS (iNOS or NOS2) is most prominently expressed by macrophages. iNOS activity and increased levels of iNOS have been found in various tumours and tumour cell lines but not in normal tissues; however, the precise role of NO in tumour progression has yet to be elucidated. We studied the expression of iNOS in paraffin sections of 41 benign naevi and 52 primary malignant melanomas (MM) of the skin, as well as in 13 metastatic MM. In addition, nitrotyrosine, indicative of NO production and formation of peroxynitrite, was studied in frozen sections of 13 naevi and 30 MM. Virtually all naevi expressed iNOS, but very few expressed nitrotyrosine, indicating either that iNOS in naevi is functionally inactive, or that naevus cells lack reactive oxygen radicals and thus do not form peroxynitrite. Normal melanocytes in adjacent uninvolved skin were unreactive for both markers. In MM, iNOS was most frequently expressed in the 'pure' and 'invasive' radial growth phase (RGP), whereas expression in the vertical growth phase (VGP) and metastatic phase occurred only in 76% of cases; moreover, in these latest phases of tumour progression, iNOS staining was weak and focal. We conclude that iNOS is expressed de novo in most benign pigment cell lesions. In MM (iNOS-generated) NO appears to play an important part in the early steps of invasion (i.e. the 'invasive' RGP), where it may stimulate neo-angiogenesis and may be a prerequisite for further tumour progression; this view is also supported by the finding of iNOS in the associated blood vessels in the papillary dermis. Finally, our data suggest that (iNOS-generated) NO plays a less significant part in the VGP and in metastatic melanoma.